Lamp failure indicator



NOV. 29, 1949 K E JR 2,489,649

LAMP FAILURE INDICATOR Filed March 1.0, 1949 MII/EN TOR, p/JUL /(/El/,Q, J2.

ATTORNEY Patented Nov. 29, 1949 UNITED STATES PATENT OFFICE 2,489,649 LAMPFAILURE ln'ptoA'ron Paul H. Kuever, Jr., Alhambra, c nt. Application March 10, 1949, saa mys o i 7 Claims.

This invention relates to electric lamps, and more particularly to a lamp of the type adapted to be energized in series with other similar lamps, as in the conventional arrangement of low-voltage lamps employed for Christmas-tree lighting. When the filament of one of the lamps insuch a series arrangement burns out, the other lamps in series with it are extinguished so that it is diflicult to determine which of the lamps is defective. To avoid this difiiculty, it is an object of my present invention to provide a lamp having improved means for visually indicating failure of its file.-

ment.

For the purpose of indicating lamp-filament failure it has been proposed to introduce ionizable gas in the lamp bulb in an amout such that a glow-discharge is produced when the voltage across the filament supports increases as a result of rupture or burn out of the filament However, the presence of such gas in the bulb has been found to have a harmful effect on the filament and tends to shorten its life. For instance, I have found that even a very small amount of neon gas in the bulb appears to reduce the temperature of an ordinary incandescent filament so that the cross-sectional area of the filament must be reduced in order to obtain normal brilliance; the filament then being sofragile that it is more subject to rupture by burn-out or shock.

It also has been proposed to provide small neon glow-lamps connected in parallel with, but physically separate from, each of the incandescent lamps of a series so that upon rupture of a lampfilament the glow-lamp lights. An obvious-disadvantage of such an arrangement is that there are more parts which may become damaged or electrically disconnected. Further, the mere loosening of the incandescent lamp in its socket will cause its associated glow-lamp to light and thereby give a false indication that the loose incandescent lamp is burnt out.

To overcome the above-mentioned disadvantages of the prior-art systems, I provide, as an integral part of the lamp, glow-discharge means for indicating filament failure, but I locate the indicating means in a sealed compartment of the bulb separate from the compartment which contains the filament. Further, I extend the filament supports or conductors into the separate compartment to serve as electrodes for the glow-discharge, so that the indication of filament failure is positive inasmuch as the glow can occur only in the event of actual rupture of the filament and resultant increase of voltage across the conductors.

For full understanding of the invention, and further appreciation of its features and advantages, reference is to be had to the following detailed description and accompanying drawing, and to the appended claims.

In the drawing:

Figure '1 is a'view, mainly in longitudinal section'; of a lamp embodying the invention;

Figure 2isa fragmentary sectional View illus trating a modified form of conductor extension; and Figure 3 is a schematic view of a series arrange-: ment of lamps of the kind shown in Fig. 1.

Referring first more particularly to Figs. 1 and Spf'the'drawing', the numeral I I indicates a'lamp having a bulb I2"of the generally pear-shaped type commonly used in Christmas-tree lighting; Attached at the bottom of the bulb is a conven-' tionalbase l3. Near the tip'of the bulb is a'par-. tition l4' which sealingly divides the bulb intoa large main compartment l5 and a relatively small compartment Iii; the partition lil conveniently being ofthe'same vitreous material as the bulb and integrally joined thereto. In production, the

' tip portion l2' of the bulb may be formedas an addition to a bulb whose top corresponds to the partitionld.

Connected in the usual manner to the contact elements of the base 13 is a pair of metallic electric conductors I! which sealingly extend'into the main compartment I5 of the bulb. Joined to the conductors l1, asby welding, is a pair of similar conductors 11', which extend upward into the small compartment [6; the material of the part1 tion" l4 being'fused around the conductors H to preserve the seal between compartments [5 and" Bridged across the'conductors ll-ll' in the' main compartment l5'is an incandescent filament [8 of the usual low-voltage type. Fused around the'conductors ll" near their upper ends is a vitreous'button l9 whose main purpose is to hold the conductors in properly spaced relation during manufacture of the lamp; the button having no particular utility in the finished lamp inasmuch as the filament-supporting conductors l'l-l'l are then rigidly held at both of their ends.

"The filament compartment I5 is fully evacu-" ated, and the upper compartment I5 is charged 7 with neon, or other gas or gases capable of producing a visible'glow when ionized. The pressure of the gas,'and' the spacing of the electrodes or" conductors ll in'compartment I5, are such that a faint but visible glow occurs around and between the electrodes when the full voltage of the electric service line is impressed across them. When the filament is intact, the high-resistance ionization path in compartment I6 is shunted by the relatively low'resistance of the filament, so

that onlya small fraction of the line voltage (insuificient to effect visible ionization) is then imassumed, lead to the lighting service supply. In the usual series arrangement for Christmas-tree lighting there are eight lamps whose filaments are therei'ore designed to operate at one-eighth of the line voltage; I01 example, thereare eight l5-volt lamps in series in a lzue-volt circuit. One of the lamps in Fig. 3 has a broken filament, indicated at 22, so that a glow discharge 23 appears in the. upper compartment of that lamp due to the fact that substantially the full line-voltage is then impressed across the conductors of the lamp. The voltage-drop across the intact filaments of the other lamps is negligible due to "the "minute amount or current 110w which produces-theglow discharge, so that there-is no appreciable heating of those filaments. 7

In rig. 2 there is shown the upper fragmentof a lamp identical with that of Fig. 1 except. that a portion or one or the conductors II is constituted by a resistor 20 01' the "carborrl type. This re sistor may have a value 01 about'dl megohm and serves to prevent theppossibility of the. build-up of excessive glow-discharge.current which otherwise might occur it the pressure of the gas isrelatively high. however, I have iound that such 8- resistor is not essential when the'gas pressureis of a low order but still sumcient for the production of a clearly-visible glow.

'lne conductors l|-| I are 7 spaced relatively widely apart in the main compartment, It to conform with the length of the. filament and are brought closer together in the small compartment It to define a suitable glow-discharge gap. Belative movement o1 the conductors ll-ll when the lamp is Jarred (which movement: might cause. damage to the filament) is. minimized due to the. fact that these conductors are firmly held ati-both ends.

If, as is customary, a decorativecoatingis applied to the outside of. the, lamp b1i1b,-the tip l2' may be 1815 uncoated withoutdetracting. romthe appearance or the lamp, sothatinthe event .of burn-out or the mamehtthe resultant glowjii'scharge can be detected more readily.

'lhe specific emnodimentsor my invention here! in shown and described are obviously. susceptible of modification without departing lrom the spirit. of the invention, andI intendthereiore to. be mm ited only by the scope or theappenued claims.

1.1 claim as my invention: 7 v ..l. An electric lamp, adaptedrto be .energized'in series with one or more. similar. lamps, comprising: a lamp bulb; a partition sealingly divining said bulb into a first andlasecond compartment;

8., pair or spaced electric, conductors sealingly ;e!; I

tending through the walloiv thebulb into one of said compartments and, sealingly and, insulatingly through said partition, into the other. of the compartments; an incandescentfilament in said first compartment and bridged across said con-e ductors, said lirst compartmentwbeingevacuated and a charge of ionizable. gasin said second come partment, the pressure of saidgas. and the space between the conductors in saidsecond compartment being such that aglowdischarge is .producible in the second compartment only .upon rupture of said filament and resultant: ihcreaseof voltage across the conductors.

2. An electric lamp, adaptedto-be energized in series with one or more similar lamps,.comprising: a lamp bulb; a partition sealingly dividing said bulb into a first and-,alsecond compartment; a,pair of spaced electric. conductorssealingly egrtending through the wall: ofthe .bu1b.iuto:said

4 first compartment and, sealingly and insulatingly through said partition, into said second compartment; an incandescent filament in said first compartment and bridged across said conductors, said 5 firstcompartment being evacuated; and a charge of ionizable gas in said=second compartment, the pressure of said gas and the space between the :conductors in said second compartment being such that a. glow discharge is producible in the I0 second compartment only upon rupture of said .filament and resultant increase of voltage across the conductors.

"3.An'elect'ric lamp, adapted to be energized in series with one or more similar lamps, comprising: a lamp bulb; 1a partition sealingly dividing said bulb intoJa. main and a relatively small compartment; 2. base attached to the part of the bulb defining v said. main compartment; a. pair of spaced electric conductors sealinglyextending fromsaid base into said main compartment and, sealingly andinsulatingly through said partition,.into saidsmall compartment; an incandescent filament in'said main compartment and bridged across said conductors, said main compartment. beingevacuated; and a chargeof ionizablegas in said small compartment, the pressure of saidgasand the. space between-the conductors in the small compartment being such that a glow discharge isproducible in the small compartment only upon rupture of said filament and resultant increaseof voltageacross the-conductors.

4. An electric, lamp, as defined in claim 3, wherein said bulb is .generally pear-shapedand said small compartment is at the small end-of the bulb.

5. An electric lamp sas defined i-n claim-3, and wherein a portion ofatleast .one of said-conductors, betweenthe-point of connection of said 0 filament' withthat conductor :and the sma1-1-com partment end of the conductor, is of high-resistivity material.

6. An electric lamp, adapted to be energized-in series with .one or :more similar lamps, comprising: an elongatedlamp bulbpa partition dividing: said bulb transverselyinto a-main andca, relatively smallcompartmenhsaid partition. beingof material similartothat of the bulb andv in tegrally joined thereto; a base-attachedto the partment; a pair of spaced electric conductors, arranged longitudinally within the bulb, sealingly extending from said .base into said-main. compartment and: sealingly: through said, partition, into saidlsmall compartment; an incandescent filament in said. main compartmenteand bridged acrosssaid. conductors, said main compartment being evacuated and a charge of ionizableegas in saidsmall compartment, the pressure of. said gas and the space between the conductors in the small compartment beingsuchthat a: glow discharge isproducible-in. the small compartment only upon rupture ofsaid filament and resultant increase of voltage across. the conductors.

'7. An electric lamp, as defined in claim :6,

wherein the spacing of said conductors'is -relatively widein said maincompartment to accom- No references cited.

. end of the bulb whichdefinessaid-maincom-'- 

